Antenna coupling system



L. A. HAZELTINE Re; 19,823

ANTENNA COUPLING SYSTEM Jan. 14, 1936.

Original Filed Nov. .4, 1950 INVENTOR 1 00/6 )7. (/a zaz'ne,

MA Y B eiuued a... '14, 1936 Q v Re. 19,823'

UNITED STATES PATENT .OFF lCE 1* v iaazs' AN'IENNA COUPLING SYSTEM Louis A. Hazeltine, Hoboken, N. 1., auignor to Haaeltine Corporation, a corporation-of Delaware Original No. 1,852,710. dated April 5, 1932, Serial No. 493,370, November 4, 1930. Application for reissue November 16, 1935, Serial No. 50,235

6 Claims. (01. 250-26) 1 This invention relates to electric coupling cirthe m. in w c event the detllnihS efleet cult arrangements for coupling a receiving capact n to become y largeity-type antenna to a thermionic tube. particu- It is One Of t e Primary Objects the P t larly a. thermionic tube constituting the first stage invention to avoid such a contingency by the addiof a muiti-stage tuned radio-frequency amplifier tion of a resistance in shunt to the input termiin which all stages are tuned by variable con- 118-15 013 the Coupling transformer P m y Windingdensers mechanically. connected by a single con- The maximum value of this resistance is chosen trol. sufilciently large to have negligible effect on the More especially the invention is directed toward Performance the circuit antennas having improvements in antenna coupling circuits of the average B than average p ity. on 10 type disclosed in United States Letters Patent No. the oth a d t s um value of hu t e- 2,022,514, granted November 26, 1935, upon the sistance is chosen sufliciently small so that it application of Wm. A. MacDonald wherein the s v s to p v nt any sharp resonance eflects in antenna is coupled to a thermionic tube by means th P y circuit (w normally resonant of a. transformer having a tunable secondary coil at about the lowest frequ y Ofthe tuning range) 15 and a primary coil coupled thereto having mwhenthe antenna'has less than average capacity. cient inductance so that it resonates with the In this way the detuning eifects reflected into capacity of an average antenna at a frequency the secondary circuit 0! the coupling t rmer slightly-below the tunable frequency range in orwhich aredue to variations in the antenna cader to increase the response at the lower tuned p y, can b held Within as close-limits as refrequencies, and thereby oifset to a desired extent quired in order to permit uni-control timing in the factors normally operative in the well known the case of a multifstage tuned radio-frequency manner toprqduce an increase in response as amplifier coupled to the antenna cillfllit. the frequency of tuning is increased. Another important function of t e resistance The consideration which limits the 'voltage connected, inaccordance with this invention, in step-up ratio obtainable between primary and. shunt to the primary. winding of the coupling secondary circuits of the coupling transformer, is r n f rm r. i to limit the response at the resoin general, the detunlng eifect of the primary cirnant frequency oi the primary circuit when the cult upon the secondary circuit when antennas ante na capac ty 18 Such 88 to Produce resonenee are employed having capacities diflering widely within ski); sligtlfifl lrwi belozlv1 the t:unable frliiequenicy 0 v from that of the average antenna. Since any range. ce'o e se e an nna coup ng crchange in antenna capacity from the average cult would be unduly responsive at the lower frevalue is reflected into the secondary circuit by ,quencies of tuning. virtue of the primary-to-secondary coupling The shunt resistance can be very conveniently eilects, it is necessary that the eifective coupling made in the form of a variable resistor or potenbetween transformer windingsbemade suihcientiy =tiometer serving to variably couple the antenna small so that the detuning eflect of the antenna circuit to the input of the couplingtransformer, is negligible. The effective coupling however' in this way providing a manually operable volume should not be reduced any further than is recontrol for adjusting the intensity or attenuation quired to eflect this end, since an unn loss of the received 818 81. This dualism! mnefloh 40 in m m would result the shunt resistance constitutes a second impor- When antennas. which have greater than averm object of this inventmnage capacity are used in t s of the t TO attain the full advantages of this invention, scrim (the present invention not being the self-inductance of the coupling transformer primary winding. the coefilcient of coupling beployed) the resonance frequency of the primary d M din d circuit is reduced and thereby removed further tween the primary and sewn n an r the magnitude of the resistance shunting the from the tuningrange oi the receiver. Hie de- M winding should have values which are tuning eii'ect therefore of a larger than average related to the trequencm to the antenna capacity antenna capacity, or even of ashort-circuit across and to the constants of the tuned secondary up 2 553 32 g iggifi cuit in accordance with rules stated below.

smautenhasmem Referringtothe drawing:

having less than average pac ty, t e reso ance Fig. lshows schematically a multi-stage tuned frequency of the primary circuit approaches the radio-frequency receiving system connected to an tuning range, and insome cases even falls antenna by means of a coupling circuit in accordance with this invention, wherein the resistance in shunt to-the coupling transformer primary winding is fixed; a

Fig. 2 shows a modification of the invention as applied .to a multi-stage uni-controlled tuned radio-frequency receiving system wherein the resistance in shunt to the antenna coupling trans- ,former primary winding is shown in the form of a potentiometer variably coupling the antenna circuit to the receiver input;

Figs. 3, 4 and 5 show other schemes, interchangeable with the antenna coupling system of Fig. 2, of employing a variable resistor or a potentiometer for variably coupling the antenna circuit to the transformer primary winding, which attain the objects of this invention.

In Fig. 1 the coupling system consists of a transformer 'T having a'primary coil L. and

secondary coil I... The primary coil is connected in parallel with the resistor 1'. between antenna A and ground G, the capacity between antenna and ground being denoted by ct.v The primary coil is magnetically coupled to the secondary Ls. the latter being connected in parallel with the tuning condenser C5 between grid and cathode of a thermionic tube V.

' This circuit may be employed by itself, in case it is desired simply to have a coupling system whose tuning adjustment may be calibratedindependently of the antenna constants, or else'itmay be iollowed by other tuned amplifying stages,

condensers of the succeeding radio-frequency either with separate tuning controls or a single tuning control. I

In the circuit of Fig. 1, however tube .V is in-. dicated as constituting the first stage of a multistage tuned radio-frequency receiving system, the

succeeding stages of which, as well as the detector and audio-frequency amplifying stages, are indicated by the rectangle B, the output of which is connected to a loud speaker H. The condenser C- is mechanically coupled to the corresponding amplifying stages by means of the uni-control element U.

The circuit arrangement for the radio-frequency amplifying stages is shown in detail in Fig. 2 wherein the successive tubes V to V2, inclusive, of a multi-stage tuned radio-frequency thermionic receiving system are inter-connected in accordance with the methods disclosed in my U'. 8. Patent No. 1,533,858 granted April 14, 1925. Instead of employing neutralized three-electrode tubes, as in this figure, it is sometimes desirable to use tubes having other means for suppressing the effects of interelectrode capacity coupling such as the screen grid of a four-electrode tube as in the remaining figures.

The resistance r. in shunt to the primary winding L. of transformer T is arranged in the form of a potentiometer with the antenna A connected to the variable tap for controlling the signal intensity impressed upon the receiver input.

The inductance of the antenna coupling transformer primary winding 1... in order to accom plish the results of the present invention, is made.

greater than or at least equal to that of the secondary winding 11:. The following notation will be employed in a detailed description of a preferred embodiment of the antenna coupling circuit:

u, angular frequency of signal, radians per micro-second; i

E-, signal voltage impressed upon the antenna, volts;

Es, voltage developed across secondary winding II, volts;

Cl. antenna capacity, millimicrofarads;

Cl, secondary circuit tuning capacity, millimicrofarads;

p, ratio of total, conductance of secondary circuit at resonance to the susceptance wC. (this, ratio has been called the natural power factor") k, coefficient of coupling between transformer primary and secondary circuits.

L actual self-inductance of primary coil, millihenries;

as measured with secondary coil in place and short-circuited, millihenries;

1., actual self-inductance of .secondary coil millihenries; r

L.=L.(1k'),- self-inductance of secondary coil as measured with primary coil in place and The value of C. is made equal to'the capacity Cu and C5: of the succeeding tuning condensers at all settings of the tuning control U, i. e. all tuning condensers are made identical. Under these conditions, and assuming that the tuning control is adjusted so that the interstage coupling circuits are in exact resonance at a desired frequency u, i. e., so that the voltage step-up ratio of the antenna coupling system is:

In deriving Equation (2), the resistance and natural capacity of the primary coil L, and the resistance and self-inductance of the antenna A have been neglected, which is legitimate with ordinary values of these quanti ies. It may be noted that although the antenna coupling system itself is not quite in tune, the deviation from exact resonance is too slight to cause a serious departure from the peak of the resonance curve when the constants are chosen in the manner described below; and this deviation is fully taken into account in the above equation.

The effective width of the frequency band covered by the antenna coupling system exceeds that covered by the secondary circuit L-C- alone, in

. iogeas the ratio of the above denominator to its value 1 when k=; that is, in the ratio This ratio is greatest when the antenna circuit is in resonance (uCaL'=1), its valve then being Now'it will be observed that the factors a and Cs occurring in the numerator of Equation (2) indicate a tendency for the voltage step-up ratio to assume a low value at low tuned frequencies and small antenna capacities. In order to increase the response under such conditions. the denominator of Equation (2) must be kept as small as posible, which can be accomplished by makingWC-L". of the order of unity at the lowest tion (2) is also of the order of unity. In this parenthesis the term lowers the step-up ratio, but by Equation (4) it also keeps the frequency band from being too tuning represents a suitable compromise, which I is sufliciently high to prevent excessive response at the resonance frequency of the antenna cira different frequency.

cult when the secondary circuit LG is tuned to The results derived from an analysis of the above equations may be embodied in the following rules:

v (I) The self-inductance of the primary coil L'. should be so chosen that it resonates with the capacity of an average antenna at about the lowest frequency to which the system is to be tuned,

preferably at a frequency which is slightly lower than the lowest tuned frequency.

' (H) The coupling coefficient between the primary and secondary circuits of the antenna coupling system should be of the order of somewhat less than the square root of the natural powe factor of the secondary circuit.

(III) 'The resistance r. shunting the primary winding La should be of the order of from three to seven times the reactance of the primary coil 1. at the lowest tuned frequency. If the resistance is adjustable, this refers to its maximum In the modii'ication of Fig. 2 it will be noted extending to the antenna A. The modification.

of Fig. 3 differs from that ofPig. 2'in that the resistance r. is serially included in the antenna circuit with the lower terminal of the coupling transformer primary winding I. connected to the grounded terminal of the resistance, and with the,

upper terminal of coil I. variably tapped In Fig. 4 the resistance n is at times bridged across the coil L with the antenna connected to the upper terminal of the resistance and the ground G variably tapped thereto. The modification of Fig. 5 differs from that of Fig. 4 by strapping the lower terminal of resistance to ground G, so that the portion of the resistance up to the variable tap is short circuited.

Capacitive coupling, which may be inherent or added in the form of a condenser between the primary and secondary transformer coils can either add to or subtract from the magnetic coupling, as described in the MacDonald patent previously referred to. Rule (II), above, gives the total coupling at the lowest frequency, which is practically all magnetic coupling. With moderate additive capacitive coupling, the voltage step-up ratio at higher frequencies will be improved, except with very small antenna capacities; but the added capacitive coupling at' its greatest value (lowest C. and lowest Cr) should not exceed the order of magnitude of the magnetic coupling.

The following values are suitable for broad-g cast reception as employed in the United States (0.55 to 1.5 cycles per micro-second) and illustrate the above rules:

(Jae-0.2 millimicrofarads, average antenna;

L'.=0.2 millihenries u=2rX0.55=3 .46 radians per microsecond;

Using these values for the constants, the voltage step-up, by Equation (2), lies between 6 and a little over 8 throughout the broadcast band of frequencies.

A disadvantage of the modification of Figs. 2 and 3 resides in the fact that the adjustable contact arm of resistance 1'. being at an ungrounded potential requires aninsulating mechanical element for adjusting the same. A further disadvantage is that with the adjustable contact set at other than the maximum position, a portion of the resistance is serially included in the resonant primary circuit IaCi thereby reducing the selectivity and otherwise introducing a detuning action due to the primary circuit impedance reflected into the turned secondary circuit L0,. This latter objection also applies to the Fig. 4 showing.

Fig. 5 is thus the preferred embodiment wherein the adjustable contact is always at ground potential, the resistance n. regardlem of the adjustment thereof being at all times entirely in shunt to the primary circuit 1-0.. with this arrangement it is obvious that adjustment of the contact arm to an intermediate point has an inappreciable effect upon the tuning of the secondary circuit.

What 'is claimed is:

1. A high-frequency coupling circuit tunable throughout a frequency range and adapted primariiy for coupling a capacity type antenna to the input of a thermionic tube, comprising, a

tunable secondary circuit having coupled thereto a primary circuit including inductance sufficient to resonate with a certain antenna capacity at a frequency fixed at about the lowest frequency of said tunable range, and shunt-resistance associated with said primary circuit sufficiently high in maximum magnitude to have an inappreciable effect upon the operation of said coupling circuit when connected to an antenna having said certain capacity, said magnitude being sufflciently low to prevent serious detuning for a given frequency adjustment of said tunable secondary circuit when said primary circuit is connected to an antenna of less than said certain capacity.

2. A high-frequency coupling circuit tunable throughout a frequency range and adapted primarily for coupling a capacity type antenna to the input of a thermionic tube comprising, a

tunable secondary circuit'havin'g coupled'thereto a primary circuit including inductance sufficient to resonate with the capacity of said antenna at a frequency fixed at about the lowest frequency of said tunable range, resistance connected in shunt to said primary circuit having a maximum magnitude of, the order of three to 'seven times the reactance of said primary-cirate with the capacity of said antenna at a frequency fixed at about the lowest frequency of said tunable range, and shunt resistance assoclated with said primary circuit, the coupling 'coefiicient between said primary and secondary circuits being of the order of somewhat less than the square root of the natural power factor of said secondary circuit.

4. A high-frequency circuit tunable throughout a frequency range and adapted primarily for coupling a capacity type antenna circuit to the input of a thermionic tube, comprising, a transformer having a secondary coil tunable by means of an associated variable capacity, and. a primary coil coupled to said secondary and having an inductance s'ufiicient to resonate with the capacity of said antenna circuit at a frequency fixedat about the lowest frequency of said tunable 'range, and a resistance in shunt to said of a maximum magnitude sufilciently large to primary coil, the coupling coefficient between said primary and secondary coils being of the order of somewhat less than the square root of the natural power factor of the tunable secondary circuit, themaximum value of said resistance being' of the order of three to seven times the reactance 'of said primary coil at the lowest frequency of said range.

5. A high-frequency coupling circuit tunable throughout a frequency range and adapted primarily for coupling a capacity type antenna circuit to the input of a thermionic tube, comprising, a tunable secondary circuit including variable capacity and a secondary transformer coil having magnetically coupled thereto a primary coil of inductance sufficient to resonate with a certain antenna capacity at a frequency fixed at about the lowest frequency of said tunable range, and resistance connected in shunt to said primary coil have an inappreciable effect upon the operation of said coupling circuit when connected to an antenna having said certain capacity, said magnitude being sufliciently small to prevent serious detuning for a given capacity setting of said tunable secondary circuit when said primary coil is connected to an antenna having less than said certain capacity.

6. A high-frequency coupling circuit adapted primarily for coupling a capacity type antenna to the input of a thermionic tube, comprising, a transformer having a secondary coil tunable throughout a frequency range by an associated variable capacity, and a primary coil of inductance sufllcient to resonate with the capacity of an average antenna at a frequency fixed at about the lowest frequency of said tunable range, and a variable resistance in shunt to said primary coil and connected to variably couple an antenna circult to said primary coil, the coupling coeflicient but a magnitude sufllciently small to prevent se- 50 rious detuning of said coupling circuit for a given setting of said variable capacity with said primary coil connected to an antenna of less than average capacity.

LOUIS A. HAZELTINE. 55 

